1. Field of Invention
The present invention relates to apparatus for cooling a continuous rolling metal product, more particularly a steel product, manufactured by continuous casting, and a method for operating the apparatus.
2. Description of Prior Art
It is known that continuous casting of a metal product is a method which consists in casting the molten metal in a bottomless mold which is usually oscillated and the walls of which are cooled energetic. The effect of the energetic cooling is that the skin of the cast metal solidifies rapidly and forms a solid crust surrounding the molten metal which forms the liquid core. The product which is partly solidified is then extracted continuously from the mold and passes through a secondary cooling zone where it finishes cooling and, consequently, solidifying.
The presence of the liquid core brings about ferrostatic pressure inside the product. This ferrostatic pressure acts from the inside on the solidified skin and can cause perforations, i.e. cracks in the skin, in the places where the skin is not adequately resistant. These weak points are the result in particular of uneven cooling or inadequate support of the product in the secondary cooling zone.
The conventional plant for a secondary cooling zone comprises support rollers and guide rollers, between which water spraying devices are disposed, for example jets.
Using equipment of this type does, however, entail two major disadvantages which can lead to the weak points mentioned above. On the one hand, the metal is only firmly held along the contact generatrices of the rollers, which constitutes a serious risk of perforation between two rollers and gives rise to convex deformations. On the other hand, the cooling jets alternate with the rollers along the path of the product. The product therefore undergoes a series of coolings and heatings, i.e. a series of thermal cycles which do not permit even cooling and consequently damage the evenness of the thickness of the solidified skin. Belgian Pat. No. BE-A-675 403 discloses a device for cooling a continuously cast metal, by means of cooling bodies used in respect of the metal product during solidification. These cooling bodies are arranged in successive pairs spaced apart. They do not ensure even and adequate cooling and continuous support of the product throughout the secondary cooling zone. Further, they are subjected to wear and they are relatively complicated to install.
German Pat. No. DE-C-21 43 962 discloses apparatus for cooling and guiding a continuously cast product, comprising a grill in the links of which jets are disposed. The grill is pressed against the solidified lateral surface of the product which it guides. In this case, there are also problems of wear of the grill and deterioration in the quality of the product surface. Furthermore, the cooling achieved is not homogeneous over the entire surface.